This application claims the priority of German Patent document 10032419.3, filed Jul. 4, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a fuel cell system and to a method for operating a fuel cell system.
U.S. Pat. No. 5,344,721 discloses a PEM fuel cell system in which product water is extracted from the cathode exhaust gas of the fuel cell and returned to a reservoir which is carried with the system. Water recovered in this manner is cleaned in an ion exchanger before it enters the reservoir, in order to reduce its conductivity before it is introduced into the fuel cell for cooling purposes.
One object of the invention is to provide a fuel cell system, and a method for operating a fuel cell system which achieve an improved water balance. This and other objects are achieved by the fuel cell system and method according to the invention, in which at least one ion exchanger unit is arranged in a flow path in which a mixture of water and an operating medium is flowing, between a condensate separator and a gas generation system for supplying the fuel cell unit with hydrogen.
The advantage of this arrangement is that in a fuel cell system which is operated with an operating medium (such as preferably hydrocarbon or an alcohol or an ether), the ion exchanger unit can be used to clean a mixture of water and the operating medium. This makes it possible to substantially prevent damage to components and lines in the flow path for the mixture caused by corrosive high-purity water, and also makes it possible to suppress harmful deposits on catalytic components.
The use of an ion exchanger unit for a water/operating medium mixture has the further consequence that the unit advantageously acts as a highly efficient mixer element and therefore improves the homogeneity of the mixture. The use of operating media which as additives in water lower its freezing point is particularly favourable, since in this way it is possible to prevent water in the fuel cell system from freezing at low outside temperatures. A particular advantage is that, when the ion exchanger unit is exposed to a mixture of this type, freezing of the ion exchanger unit is also suppressed, since this phenomenon can make the ion exchanger unit unusable.
The invention is particularly suitable for fuel cell systems in mobile units, such as for example fuel cell vehicles, although it is also suitable for stationary systems.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.